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One of the strongest rocks in the world is one that you might not expect, and the story of how it formed deep under the earth is intense!

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[ INTRO ].

Today, Squeaks and I are looking at all kinds of super strong rocks! We can test which rock is harder by scratching one rock against another, and seeing which one doesn’t leave pieces behind.

Hmmm … this rock isn’t so strong because it leaves some pieces behind when I scratch it against this second rock, see? And the second rock is stronger because it doesn’t crumble. One of the strongest rocks of all though, is one that you might not expect.

It’s a diamond. [Squeaks asks if diamond is really a rock]. You’re right, Squeaks! Diamonds aren’t exactly the same thing as rocks.

A diamond is something called a crystal. That means it’s solid, and when you look /reallllly/ close, like with a special microscope, you can see that it’s made up of smaller pieces arranged in a special, repeating way. Rocks, on the other hand, are made up of lots of different crystals mixed together — like the rocks we have here.

If you mixed together a diamond and a bunch of other crystals, then it would be a rock. But diamonds are stronger than all the other rocks and crystals in the world! That’s because of the stuff diamonds are made out of, and how they form.

Let’s take a closer look. Diamonds are made out of carbon, a special material that makes up all kinds of things here on Earth. Lots of rocks contain carbon, pencils and paper have carbon in them, and every single living thing has carbon in it, even you and me.

But carbon looks different depending on what other materials it’s put together with, and how they’re put together. It’s a lot like how you can make lots of different things with building blocks. If Squeaks puts the same blocks together in different ways, they can be a tree, or a house, or a mountain.

For carbon building blocks to become a diamond, they need to be heated up really high, and smushed together super hard. Most diamonds formed a really long time ago — between 1 and 3 billion years! That’s way before there were dinosaurs on Earth.

There weren’t even any plants yet! Most diamonds also formed deeeeeep underground. About 150 kilometers down — way farther than the deepest hole anyone has ever dug — the Earth is incredibly hot, and made of melted rock.

It’s a bit like the inside of a volcano. Some of the carbon deep down there was heated up really, really hot, and was squished together by all of the stuff on top of it. We call that squishing pressure.

With all of the heat and pressure around it, the tiniest bits of carbon began to move around and stick together, holding each other in place until there were bigger pieces of carbon all stuck together. Can you guess what those bigger pieces turned into, Squeaks? [Squeaks guesses a diamond]. That’s right, it was the start of a diamond.

Because of the heat and the pressure, the carbon stuck together in a very regular pattern. That’s a big part of what makes diamonds so strong. But even after the carbon stuck together to make the diamonds we know today, they were still really far underground.

Then something amazing happened. Some of the molten-hot insides of the Earth /erupted/ towards the surface. [Squeaks squeaks in surprise]. It was just like a volcano, Squeaks, only these eruptions came from even deeper underground that volcanoes today, and happened much faster.

The eruptions carried all kinds of materials from the inside of the Earth up to the Earth’s crust, the ground right near the surface of the Earth. The diamonds were carried up, and when they reached close enough to the surface of the. Earth, the diamonds and all of the burning-hot rocks and other stuff around them cooled down.

Many of the diamonds stopped a little bit below the surface, and even after they cooled down, they stayed in their special shapes. Billions of years passed, until people started to find diamonds in the ground. These days, people dig up diamonds to sell and to use in things like jewelry or special tools that need to be made of one of the strongest materials in the world.

That is one super crystal. Thanks to one of our viewers, Rishabh, for asking us about this! What amazingly strong rocks can you find where you live?

Are there other tests you can think of to see how strong rocks and crystals like diamonds are? We have a website where you can send us your ideas! Just ask a grown-up to help you go to to check it out.

We’ll see you next time, here at the Fort! [ OUTRO ].